1. Field of the Invention
This invention relates to a method of automatically printing color photographs, and more particularly to a method of automatically making prints from color negatives and positive originals (hereinbelow referred to as "originals") with exposure control. More specifically, the exposure in a color printer is controlled based on the measured color balance and density at points of the original which are of flesh color.
2. Description of the Prior Art
In determining exposure in color printers, various methods have been known and practically employed. A well-known printing system in which the printing light source intensity is adjusted during red, green and blue exposures to levels which will normalize the resulting integrated transmittances to a near-neutral color balance, i.e., "gray ", is based on U.S. Pat. No. 2,571,697, Evans. This printing system produces satisfactory results from a large majority of the negatives of a given type of film. It has also been known in the art to adjust the rate of correction for red, green and blue exposures based on a linear combination of the red, green and blue large area transmission densities (LATD) of the original to be printed.
Since the above described conventional printing systems are based on the integrated transmission measurements conducted over the whole area of the original, the obtained prints are not always satisfactory. For instance, if the background of the principal subject matter is primarily red (red curtain or furniture), green (green grass of foliage) or blue (blue sky or water), color correction based only on the aforesaid LATD system is unsatisfactory. This problem is known as "color failure".
Further, if the background of the principal subject matter is of particularly high or low brightness, the conventional correction based on the integrated transmission density does not give satisfactory results. For example, when the principal subject matter has been photographed with a back light or in a spotlight conventional correction will give unsatisfactory results. This is known as "density failure".
According to the inventors' tests, in the color printing process using the LATD printing system the yield of satisfactory prints is about 70% of all the prints obtained.
It has also been known in the prior art to determine the exposure in a color printer based on the measured densities of divided areas of color originals in which the entire area of the original is divided into upper and lower, right and left, and central and peripheral sections. The exposure is determined based on a combination of the LATD and the densities of the divided areas. In this system, the yield of satisfactory prints is somewhat raised. However, since the density of the principal subject matter is not accurately measured in this system, the correction is not always effected in the most desirable manner.
According to the inventors' investigation, about 80% of the color originals have figures as the principal subject matter. Further, in looking at printed color photographs, it is well known that most people are concerned about the faces of the figures. Therefore, in printers, it is desirable that the faces of the figures be printed in a good condition. An exposure controlled to obtain a good flesh color in the areas of flesh color might be improper for areas other than the flesh color areas. However, even so, the yield of satisfactory prints is higher, if the exposure control is based on the flesh color areas.
Thus, it is proposed to print color originals based on the flesh color areas when the originals contain over a certain number of points of flesh color. If the originals have no areas of flesh color, the exposure may be controlled according to the conventional LATD printing system or the like.